Fluid Dynamics
A source-term interpretation of turbulent rough wall-pressure spectra
J. M. O. Massey, A. J. Smits and B. J. McKeon
Wall-pressure fluctuations beneath a turbulent boundary layer drive the flow-induced noise and structural loading of rough surfaces. On a smooth wall their variance grows with the logarithm of the Reynolds number, a growth carried, in a source-term reading, by the nonlinear
turbulence–
turbulence part of the pressure source acting across the logarithmic layer. We ask what sets the same growth once the wall is fully rough. Standard rough-wall phenomenology answers it: above the roughness the mean flow keeps its smooth-wall logarithmic form, so the active source range is cut off at the roughness height rather than the viscous length, and the variance grows on the logarithmic span between the roughness height and the layer thickness in place of the Reynolds number. Splitting the pressure source into its two physical parts then distinguishes separate contributions to the energy: a roughness-local one from the mean-shear source, fixed at high frequency on the roughness scale, and an energetic one from the nonlinear source at the outer scale, which alone carries the growth. Calibrated against rough-wall cases, the model collapses the spectral shape onto this energetic peak and holds it Reynolds-independent at fixed geometry. The canopy contribution decays with distance from the wall and contributes a finite offset. The growth coefficient is predicted to be the smooth-wall one. The present range is too narrow to discriminate that rate from twice or half it, so the contribution is a parameter-free prediction and the identification of a suitable roughness-size sweep that would test it.
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Mathematical Physics
Asymptotic analysis of a Fredholm determinant occurring in the description of the dynamical correlation functions of the Lieb–Liniger Bose gas
Frank Göhmann, Karol K. Kozlowski and Mikhail D. Minin
We perform a large-$x$ asymptotic analysis of the Fredholm determinant of an integrable integral operator with generalized sine kernel, where $x$ controls the strength of the oscillations along the integration contour of the operator and will play the role of the distance variable in applications to the correlation functions of integrable
quantum systems. Our generalized sine kernel involves a number of functional parameters that will allow us to adapt it to the analysis of the dynamical correlation functions of the Lieb–Liniger model at finite temperature and for all positive values of the coupling constant. It will also allow us to consider a class of
equilibrium correlation functions that are governed by generalized Gibbs ensembles. Our work is based on the analysis of a
matrix Riemann–
Hilbert problem that is canonically connected with our integrable integral operator.
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Strongly Correlated Electrons
Resolving the Magnetic Ground State and Field-Induced Transitions in Magnetic Dirac Semimetal Candidate EuMnSb$_2$
Yiu-Fung Chiu, Jian-Rui Soh, Sanjay Sharma et al. (+9 more)
The
magnetic structure of a
magnetic topological semimetal EuMnSb$_2$ is investigated in fields up to 30 T using polarized and unpolarized
neutron diffraction, pulsed-field x-ray
magnetic circular dichroism and pulsed-field magnetometry. We determine the zero-field
magnetic structures of the Eu and Mn sublattices, and find that
magnetic transitions induced by applied fields below 2 T correspond to changes in the
magnetic order of the Eu
spins alone without detectable perturbation to the order of the Mn
spins. An additional
magnetic transition is observed at fields close to the saturation field for the Eu
spins. We present a mean-field model which describes key features of the
magnetic behavior and allows us to estimate the dominant Eu–Eu and Eu–Mn exchange interactions responsible for the coupling between magnetism and electronic
topology.
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All authors Yiu-Fung Chiu, Jian-Rui Soh, Sanjay Sharma, J. Alberto Rodríguez-Velamazán, John Singleton, Eugen Weschke, Oleksandr Prokhnenko, Oksana Zaharko, Dharmalingam Prabhakaran, Stephen J. Blundell, Paul A. Goddard, Andrew T. Boothroyd
General Relativity and Quantum Cosmology
Non-exotic traversable wormholes in Einstein-Chern-Simons gravity
Mauricio Cataldo, Fernando Goméz, Paola Meza et al. (+2 more)
We investigate traversable wormhole solutions in five-dimensional Einstein-Chern-Simons (EChS)
gravity, a gauge-theoretic extension of General Relativity that introduces a higher-
curvature correction parametrized by the combination $\alpha l^2$, where $\alpha$ is a dimensionless coupling and $l$ is a length scale. Working with the Morris-Thorne metric and an anisotropic fluid, we derive exact expressions for the energy density, radial pressure, and lateral pressure at the wormhole throat. We show that the radial Null Energy Condition (NEC) is satisfied at the throat if and only if $\alpha l^2\leq-r_0^2$, being saturated at $\alpha l^2=-r_0^2$ and strictly satisfied for $\alpha l^2<-r_0^2$, independently of the shape function. In the latter regime, the energy density is strictly positive and the full NEC, Weak, Strong, and Dominant Energy Conditions can be simultaneously satisfied. These results are established analytically for arbitrary shape functions and illustrated concretely for the power-law family $b(r)=r_0(r_0/r)^n$, $\Phi=0$, for which all four standard energy conditions are satisfied at the throat for all $n>0$ when the EChS coupling is sufficiently negative. We further show that the radial pressure is negative and geometrically fixed at the throat, independently of $\alpha$, $b(r)$, and $\Phi(r)$. Using the Volume Integral Quantifier (VIQ), we establish that the EChS correction reduces the magnitude of the negative integrated NEC contribution relative to GR, and derive an exact closed-form critical coupling $\alpha l^2_{\rm crit}$ at which the VIQ vanishes. The hierarchy $\alpha l^2_{\rm crit}<-r_0^2<0$ shows that NEC satisfaction at the throat and a non-negative global VIQ are compatible but distinct conditions, both achievable within EChS
gravity. All results reduce continuously to those of GR in the limit $l\to0$, confirming the consistency of the framework.
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All authors Mauricio Cataldo, Fernando Goméz, Paola Meza, Cristian Quinzacara, Patricio Salgado
Mesoscale and Nanoscale Physics
Reduced vortex descriptors linking polycrystallinity in magnetic nanoparticles with polarized magnetic small-angle neutron scattering
M.P. Adams, J. Leliaert, A. Michels et al. (+1 more)
Analytical
vortex models reduce polarized
magnetic small-angle
neutron scattering (SANS) from nanoparticle ensembles to a small set of texture descriptors. In this work, we apply this reduction to micromagnetic simulations of polycrystalline iron
oxide nanoflowers at a fixed particle size and examine how a controlled parametrization of multigrain disorder is reflected in the remanent descriptors. The particles are represented by explicit Voronoi microstructures, and intraparticle disorder is varied through the intergrain exchange coupling and anisotropy-axis coherence. Fitting each remanent magnetization state to a
hyperbolic vortex model reveals a predominantly two-channel organization: the intergrain exchange coupling is associated mainly with the radial
vortex profile, whereas the anisotropy-axis coherence is associated mainly with the orientational moment of the
vortex-axis distribution. The normalized
spin-flip SANS cross sections are accurately represented by independent fits of the analytical linear-
vortex SANS expression obtained from the first-order expansion of the
hyperbolic profile. The fitted orientational descriptor agrees closely with its independent real-space estimate, whereas the corresponding radial descriptors exhibit a strong global nonlinear relation. This separation identifies which information from the micromagnetic
vortex textures is robustly retained by the reduced analytical representation.
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All authors M.P. Adams, J. Leliaert, A. Michels, E.M. Jefremovas
Disordered Systems and Neural Networks
Exact mobility rings in non-Hermitian quasiperiodically decorated Lieb lattices
Ming-Jie Tao, Yi-Ting Wang, Jing Li et al. (+3 more)
The mobility ring (MR), a critical boundary in the complex energy plane separating extended and localized states, is fundamental to understanding the Anderson transition in non-Hermitian (NH) disordered systems. While MRs have been extensively studied in one-dimensional (1D) NH quasiperiodic models, rigorous analytical frameworks beyond 1D remain critically scarce. Here, we investigate a class of two-dimensional (2D) quasiperiodically decorated Lieb
lattices (QDLLs) featuring complex incommensurate potentials selectively applied to the
lattice vertices. By exactly mapping these 2D structures onto NH generalized Aubry-André-Harper (AAH) models and leveraging extended-localized transition point, we analytically derive the Lyapunov exponents and obtain exact expressions for the MRs. These exact theoretical boundaries are strongly corroborated by numerical computations of wavefunction fractal dimensions and real-space probability distributions. Furthermore, we reveal distinct evolutionary behaviors of the MRs driven by the quasiperiodic potential strength: systems characterized by $\kappa=2$ possess a single MR, whereas systems with $\kappa=3$ undergo a dynamic sequential
evolution from a single integrated ring into two independent rings. We hope that our exact results of MRs in 2D will benefit the study of Anderson localizations and MRs in high-dimensional NH systems.
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All authors Ming-Jie Tao, Yi-Ting Wang, Jing Li, Hongsheng Hou, Xiang-Ping Jiang, Lei Pan
Mesoscale and Nanoscale Physics
Engineering two-qubit gates via anisotropic exchange in germanium spin qubits
Leonardo Massai, Bence Hetényi, Eoin G. Kelly et al. (+14 more)
Germanium hole
spin qubits are a promising and versatile platform for
quantum computation and simulation. In this system, strong
spin-orbit interaction (SOI) renders the single-
qubit $g$-tensor anisotropic and electrically tunable, enabling operational sweet spots with reduced noise sensitivity. SOI also transforms the isotropic two-
qubit exchange coupling into an anisotropic tensor whose geometry is inherited from the single-
qubit $g$-tensors and
spin-flip tunnelling. Here, using two hole
spin qubits in a strained-germanium
quantum well and full vector control of the
magnetic field, we map this exchange tensor, separate it into longitudinal and transverse components, and show that they govern controlled-phase and SWAP-like dynamics, respectively. We find that the longitudinal exchange can be tuned via the
magnetic field orientation from a conventional positive value, through zero, to an effectively negative one, as measured by inverted exchange-split
spin transitions. The
magnetic field direction thus provides continuous control over the interaction
Hamiltonian: at a point of purely transverse exchange, we engineer a single-pulse baseband iSWAP, unattainable under isotropic exchange. Linking $g$-tensor geometry to exchange anisotropy establishes native
Hamiltonian engineering, enabling
spin-based
quantum simulation and gate sets selected by the global field orientation alone.
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All authors Leonardo Massai, Bence Hetényi, Eoin G. Kelly, Inga Seidler, Konstantinos Tsoukalas, Michele Aldeghi, Alexei Orekhov, Lisa Sommer, Marta Pita-Vidal, Uwe von Lüpke, Stephan Paredes, Stephen W. Bedell, Felix J. Schupp, Matthias Mergenthaler, Gian Salis, Andreas Fuhrer, Patrick Harvey-Collard
Instrumentation and Detectors
The ASD2 Chip for the Upgrade of the ATLAS MDT Chamber Readout at HL-LHC
S. Abovyan, A. Baschirotto, V. Danielyan et al. (+8 more)
Upgrading the ATLAS detector for operation at the High-Luminosity LHC requires a new, more se-lective trigger scheme to control the readout of MDT drift-tube chambers by incorporating RPC trigger information. This necessitates replacing the MDT readout electronics, including the front-end boards that house the ASD amplifiers and the custom-designed TDC. The latter buffers timing measurements for transmission to a chamber-mounted data concentrator (CSM), which, in turn, communicates with the MDT Data Processor, where MDT tracking data are combined with RPC timing information, to specifically identify high-energy
muon tracks. In this article, we report on the new ASD2 preamplifier, discussing its architecture, design details, functionality and measured performance. We also present test results for chips from MPW runs, the engineering run and the volume production of 80,000 chips. Unlike the ASD1 preamplifier, currently used for MDT readout, which relies on 500 nm chip tech-nology, the ASD2 is manufactured using the more advanced 130 nm technology. This offers a range of technical improvements that enhance critical performance parameters such as signal rise time, noise levels, and the reproducibility of threshold settings across a chip's channels. Comparative measurements are presented to verify this improved performance. Finally, we discuss the robust-ness of ASD2 against environmental conditions like radiation exposure and potential high-voltage discharges within the MDT drift tubes.
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All authors S. Abovyan, A. Baschirotto, V. Danielyan, M. Fras, O. Kortner, S. Kortner, H. Kroha, M. de Matteis, F. Resta, R. Richter, Y. Zhao
Mesoscale and Nanoscale Physics
Proximity-induced superconductivity in a bilayer graphene quantum point contact
Clara Galante-Agero, Christoph Adam, Artem O. Denisov et al. (+9 more)
We report the realization of a gate-defined
quantum point contact (QPC) in
bilayer graphene proximitized by a single aluminum superconducting electrode. Superconducting correlations induced in the ballistic channel enhance the conductance plateaus beyond their normal-state values. In addition, we observe a pronounced above-gap conductance anomaly which serves as a spectroscopic signature of the loss of superconductivity and the associated collapse of the Andreev excess current. By reconstructing the nonlinear current-voltage characteristics, we find that the magnitude of the excess current increases as successive QPC modes are populated. Additionally, we find that the switching current associated with the loss of superconductivity follows the underlying mode structure of the QPC, exhibiting discrete levels consistent with a heat dissipation-driven transition. These results demonstrate that the one-dimensional transport modes of the QPC govern both the
equilibrium proximity effect and the non-
equilibrium dynamics of the hybrid system.
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All authors Clara Galante-Agero, Christoph Adam, Artem O. Denisov, Jonas D. Gerber, Markus Niese, Alexandra Mestre-Torà, Marta Perego, Jessica Richter, Takashi Taniguchi, Kenji Watanabe, Klaus Ensslin, Thomas Ihn
Quantum Physics
Time-optimal quantum gates with bang-bang control in multilevel systems
Valentín Reparaz, Santiago Ferreyra, María José Sánchez et al. (+2 more)
We determine the optimal
quantum manipulation protocols for implementing high-fidelity, fast single-
qubit gates. We demonstrate that the time-optimal pulse sequence is a “bang-bang” sequence: discrete pulses of either positive or negative maximum amplitude or zero. The non-adiabatic bang-bang pulse sequence minimizes gate duration providing a speedup for low-frequency architectures. We first derive the protocol for a transversally driven two-level system, extracting exact analytic expressions for minimum gate times. We then extend this framework to general multilevel architectures, identifying conditions that enable the coherent suppression of leakage errors. Using the fluxonium
circuit as a representative case study, we optimize $X/2$ and $Y/2$ gates through a combination of discrete bang sequences and continuous waveform smoothing. This approach preserves near-optimal execution speeds while mitigating transitions outside the computational subspace. Open-system simulations demonstrate that these sequences outperform commensurate and resonant pulse schemes across different fluxonium regimes, achieving low-error manipulation significantly faster than standard resonant control, even in the presence of $1/f$ flux noise and dissipation.
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All authors Valentín Reparaz, Santiago Ferreyra, María José Sánchez, Daniel Domínguez, Leandro Tosi
Applied Physics
Impact of Nonlinear Absorption on Energy Distribution During FLASH-Like Deposition
Bo-Rong Lin
FLASH radiotherapy for tumors has proven highly effective in preserving normal tissue; however, the physical origin of its biological selectivity has yet to be elucidated. This study developed a minimal
diffusion-absorption model to examine the effects of nonlinear energy absorption on the spatial distribution of energy during FLASH-like deposition. Simulations revealed that nonlinear absorption alters the transfer of energy through the system while reducing the amount of energy absorbed in surrounding, unexposed regions. This behavior qualitatively resembles the tissue-sparing effect observed in FLASH radiotherapy. Parameter-space analysis revealed that the effect of incident pulse intensity depends on the absorption properties of the material, including its saturation behavior and energy threshold. These results suggest that energy-deposition conditions should be matched to the absorption characteristics of the target material.
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Quantum Physics
Superposition of dynamics, indefinite causal order, and quantum histories
Charis Anastopoulos and Ntina Savvidou
The process-
matrix formalism describes
quantum processes without assuming a fixed global causal order, but the physical meaning of indefinite causal order remains open. We address this question within histories theory, where temporal ordering and dynamical
evolution are distinct structures. We show that the decoherence functional admits coherent superpositions of dynamics. In measurement settings, under suitable factorization conditions, these generate process
matrices. In the bipartite setting considered here, process-
matrix indefinite causal order is thereby identified as an operationally restricted realization of the more general phenomenon of superposition of dynamics. Histories theory also admits a distinct kinematical notion of indefinite order, in which the ordering of physical events is itself a history observable. The resulting distinction between event order and intervention order clarifies the relation between indefinite causal order,
quantum dynamics, and spacetime structure.
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Mathematical Physics · Cross-listed from math.DG
Atiyah's Minkowski Space Conjecture Fails for Every $n\ge3$
Ziran Liu
Atiyah's Minkowski-space version of the configuration-of-points construction assigns to an admissible marked configuration of $n$ worldlines a collection of $n$ binary forms of degree $n-1$, whose roots are the ordered retarded celestial directions. He conjectured that these forms are always linearly independent. We disprove this
conjecture for every $n\ge3$. For $n=3$, an explicit planar one-parameter family yields a real coefficient determinant with exactly one simple zero in a specified interval. At this parameter, all six ordered celestial roots are distinct and the coefficient
matrix has rank exactly two. A null-translation construction then multiplies the first three forms by a common factor and produces counterexamples for every $n>3$. Consequently, within the class of complete pairwise disjoint timelike affine lines, universal independence holds at $n=2$ and fails for every $n\ge3$; for each of the counterexamples, the normalized Atiyah–Sutcliffe determinant is defined and vanishes.
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Fluid Dynamics
Intermittent turbulence in inclined gravity currents
Lianzheng Cui, Graham O. Hughes and Maarten van Reeuwijk
Inclined
gravity currents on shallow slopes can exhibit pronounced
turbulence intermittency. Using direct numerical simulations, we investigate this behaviour for a temporal
gravity current over a range of initial Reynolds numbers $Re_0$. For $Re_0=2500$ and a slope angle of $0.5^\circ$, the outer layer of the current exhibits large excursions in
turbulence intensity and repeated transitions between turbulent and weakly turbulent states. Analysis of the flow energetics reveals that the intermittency is associated with a finite delay between shear production and dissipation of turbulent kinetic energy. During transitional phases, this delay permits a transient amplification of
turbulence, which significantly weakens the mean shear by extracting kinetic energy from the mean flow and promoting entrainment-driven layer growth, ultimately leading to relaminarisation. Increasing $Re_0$ reduces the delay and progressively suppresses intermittency, steering the flow towards a more sustained turbulent state. Motivated by these observations, we develop an autonomous delay-differential model based on the coupled
evolution of the mean and turbulent kinetic energies. The model reproduces the observed transition from intermittent to sustained
turbulence as the delay is reduced and predicts an increased tendency towards intermittency at larger flux Richardson numbers. The results support an interpretation of intermittent
turbulence in inclined
gravity currents as a delay-induced oscillation arising from the finite adjustment time of
turbulence to changes in the mean flow.
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Lattice Field Theory
Configurational Temperature in the 3D XY Model
Kutloano Nkojoana and Anosh Joseph
We investigate the configurational temperature
estimator as a diagnostic tool for Monte Carlo and Langevin simulations of the three-dimensional XY model with an imaginary chemical potential. This
estimator depends only on the field configurations. It provides a stringent internal consistency check for numerical sampling
algorithms. We perform simulations using both real Langevin dynamics and the Metropolis Monte Carlo
algorithm on an $8^3$
lattice across a range of coupling values, $\beta = 0.2 - 0.7$. Our results for the action density are in excellent agreement with strong-coupling expansion predictions at small $\beta$, providing an important validation of both simulation approaches. The measured value of the configurational temperature
estimator shows good agreement with its expected value of unity in the symmetric phase. However, systematic deviations appear in the ordered phase. We attribute these deviations primarily to finite-size effects and discretization artifacts associated with the relatively small
lattice volume. Our results demonstrate that the configurational temperature
estimator provides a valuable diagnostic for assessing thermalization and algorithmic correctness in
lattice field theory simulations. Such diagnostics are particularly important in preparation for studies at real chemical potential, where sign problems arise and conventional validation methods become less reliable.
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Quantum Physics
Crossover from Fast Scrambling to Operator Confinement Tuned by an Auxiliary Qubit
Ryan Buechele, Joseph Szabo and Nandini Trivedi
We demonstrate a static, disorder-free
spin chain
Hamiltonian which, by tuning the coupling to an auxiliary
qubit, realizes a crossover between super-ballistic, ancilla-accelerated scrambling and sub-ballistic operator confinement. Our minimal model is the mixed-field Ising chain with a
spin-1/2 ancilla coupled to its longitudinal magnetization. The ancilla mediates an effective all-to-all interaction which accelerates operator spreading and
entanglement growth when weakly coupled, but rapidly saturates its
entanglement and projects
spin chain operators into effectively frozen subspaces when the ancilla coupling is strong. We locate this crossover independently through both a divergent peak in the mutual-information saturation time near $\lambda_c N/h \approx 8$ and an exponential suppression of the late-time OTOC growth rate, $\log\alpha \propto 1/\lambda$. Through a Feshbach-Fano projection and Schrieffer-Wolff transformation, we reveal an effective hidden
symmetry on the chain which confines operators on the chain for a time exponential in the coupling strength. This reconciles the fast, $\log(N)$ scrambling reported for random-
unitary-
circuit realizations of the
star geometry with the confinement previously found in its time-independent
Hamiltonian analog, showing both emerge from a single
Hamiltonian family as a function of one dimensionless parameter.
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Atomic Physics
Sensitivity Scaling and Limits of Cavity Enhancement in Miniaturized Optically Pumped Magnetometers
Christopher H. Kiehl, María Hernández Ruiz, Cristina Sastre Jachimska et al. (+1 more)
The sensitivity of miniaturized optically pumped magnetometers (OPMs) is limited by weak atom-light coupling, which an optical cavity can enhance. In this work, we model the
photon-shot-noise-limited sensitivity of cavity-enhanced OPMs in the regime of strongly collisionally broadened optical transitions, characteristic of buffer-gas-filled miniaturized vapor
cells. The cavity enhancement is benchmarked against a single-pass free-induction-decay OPM employing Faraday-rotation readout, with the probe power and detuning jointly optimized using the Cramér-Rao lower bound as a figure of merit. For a Fabry-Pérot cavity, we compare side-of-fringe, homodyne, Pound-Drever-
Hall, and Faraday-rotation readout. All four yield an optimal sensitivity enhancement scaling as $\alpha\sqrt{2\mathcal{F}/\pi}$, where $\mathcal{F}$ is the cavity finesse and $0.5\leq \alpha \leq 1$ is a readout-dependent prefactor. The enhancement is maximized at critical coupling, and we quantify its degradation away from this point. We further show that, despite
spin-dependent absorption associated with the ensemble's vector polarizability, near-critical coupling can be maintained throughout
spin precession at arbitrary finesse by exceeding a derived probe-power threshold and increasing the atomic detuning with finesse. We also establish a limit to the maximum cavity enhancement set by vector light-shift noise.
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All authors Christopher H. Kiehl, María Hernández Ruiz, Cristina Sastre Jachimska, Morgan W. Mitchell
Cosmology and Nongalactic Astrophysics
Halo Mass of ULIRGs at Cosmic Noon
Jun Pan, Ming Li, Cheng Cheng et al. (+1 more)
We present a clustering analysis of $\sim 3000$ ultraluminous infrared
galaxies (ULIRGs) at $z\sim 2$, uniformly selected by $24\mu {\rm m}$ flux and IRAC colors in the COSMOS and BOOTES fields. We measure the angular correlation functions of ULIRGs in both fields and fit them with
galaxy clustering models. Linear theory modeling shows that these ULIRGs reside in dark matter
halos with characteristic masses of $\log M_{\rm h} /({h^{-1}\rm M_{\odot}}) = 12.64\pm 0.50$ in COSMOS and $12.72\pm 0.13$ in BOOTES. The
halo occupation distribution (HOD) modeling yields occupation-weighted effective
halo masses of $\log M_{\rm eff} /({h^{-1}\rm M_{\odot}}) =12.50^{+0.26}_{-0.28}$ for COSMOS and $12.89^{+0.11}_{-0.12}$ for BOOTES. These host
halos are expected to evolve into
halos with masses of $\sim 10^{13.6-13.9}\ {h^{-1}\rm M_{\odot}}$ at $z=0$. The HOD fits allow for a non-negligible satellite contribution to the clustering of
galaxies in the BOOTES field, but the satellite fraction derived in the COSMOS field appears nearly zero.
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All authors Jun Pan, Ming Li, Cheng Cheng, Jasheng Huang
Astrophysics of Galaxies
Two domains of extended Lyman-alpha emission around galaxies: from local radiation to environmental regulation
Daria Kozlova, Lutz Wisotzki, John Pharo et al. (+7 more)
We examine the relation between extended Ly$\alpha$
halos around high-
redshift galaxies and the main factors responsible for driving the emission in such
halos, in particular at distances around and beyond one virial radius $r_\mathrm{vir}$. To reach the required surface brightness sensitivity we take advantage of the MUSE eXtremely Deep Field (MXDF) survey, allowing us to probe levels as faint as $\sim 10^{-20}$ erg cm$^{-2}$ s$^{-1}$ arcsec$^{-2}$ in individual Ly$\alpha$
halos. Our sample consists of the 21 apparently core- and
halo-brightest (yet intrinsically low luminosity $\log_{10}$L$_{\mathrm{Ly}\alpha} < 42.3$ erg s$^{-1}$) Ly$\alpha$ emitters (LAEs) in the MXDF at $3<z<4$, with typical virial radii around 20 kpc. We measure their radial surface brightness profiles out to 50 kpc (more than $2r_{\mathrm{vir}}$) and investigate the correlations between surface brightness and internal (
star formation rates of the host
galaxies, SFR) or external influences (environmental density, $\delta+1$). We find a clear break in these correlations at radii around or just below $1r_{\mathrm{vir}}$. Below this break the emission correlates tightly with SFR (as expected) and not at all with $\delta+1$. Beyond $\sim 1r_\mathrm{vir}$(20 kpc) we observe the opposite trend with no dependence on SFR, but an emerging correlation with $\delta+1$. We compare our measurements with the expected integrated surface brightness from ultrafaint, individually undetected LAEs and find that the latter is insufficient to drive the observed correlation. We conclude that Ly$\alpha$ emission from the outer
halos is regulated by the surrounding environment, but originates mostly from diffuse gas rather than discrete sources.
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All authors Daria Kozlova, Lutz Wisotzki, John Pharo, Tanya Urrutia, Ramona Augustin, Yucheng Guo, Haruka Kusakabe, Joop Schaye, Daniil Smirnov, Ismael Pessa
Mesoscale and Nanoscale Physics
Topological insulator realization induced by fermionic interaction through BF mediators
G. B. de Gracia, R. da Rocha, A. A. Nogueira et al. (+1 more)
This paper demonstrates that ordinary
fermions, interacting via a BF mediator, form a renormalized structure with non-trivial topological properties. We explore the analogy between the renormalized
fermion and a subset of real three-dimensional topological
insulators (TIs) in the vicinity of their single Dirac cones. Using the typical magnitude of TI
lattice and gaps, we constrain model parameters. The topological structure induced by radiative corrections enters a class of modified Dirac equations, ensuring the existence of helical gapless near-boundary modes. We derive an effective potential for inter-quasi-particle interactions that incorporates finite-size effects in the axial direction, revealing signatures of
spin-orbit coupling and time-reversal invariance. Remarkably, particles with different
spins do not interact via the characteristic
spin-orbit coupling, and a non-central
spin-dependent force arises. We also address the behavior of the system in the phase transition associated with the thin-film limit.
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All authors G. B. de Gracia, R. da Rocha, A. A. Nogueira, M. A. C. de Barcelos
High Energy Astrophysical Phenomena
Collisionless Shock Driven by a Supersonic Velocity Shear
Kazuki Kamiido and Yutaka Ohira
The long-term
evolution of a relativistic collisionless velocity shear in an unmagnetized electron-positron
plasma is investigated using a first-principle particle-in-
cell simulation. The Alves instability converts the shear kinetic energy into thermal and
magnetic field energy. The resulting pressures push the
plasma, leading to the formation of collisionless shocks. The generated collisionless shocks would accelerate high energy particles, which is a possible solution to the injection problem of shear acceleration. In addition, the collisionless shocks generate a
magnetic field
turbulence that is required for the shear acceleration to work.
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Instrumentation and Methods for Astrophysics
Galaxy Morphology Classification: Uncertainty Modeling and Out of Distribution Detection
Prem Prakash, Shantanu Desai and P.K. Srijith
We present a comprehensive framework for
galaxy morphology classification that combines enhanced “out-of-distribution (OOD)” detection with improved uncertainty quantification. Using “
Galaxy Zoo DECaLS”, we trained a ResNet-34 architecture under three configurations: standard cross-
entropy loss as a baseline, IsoMaxPlus loss function for OOD detection, and hybrid IsoMaxPlus+MonteCarlo Dropout for enhanced uncertainty quantification. IsoMaxPlus replaces the conventional SoftMax logits with distance-based class representations, preserving inter-class separability and enabling reliable OOD detection, without requiring additional architectural modifications or hyperparameter tuning. Coalescing IsoMaxPlus with MC Dropout provides a fast
Bayesian approximation by performing multiple
stochastic forward passes during inference. Our results show that IsoMaxPlus substantially improves OOD detection, increasing TNR@TPR95 by nearly $90\%$ relative to the cross-
entropy baseline, while maintaining a competitive accuracy of 97% across nine morphological classes. Additionally, with MC Dropout, the model yields more stable predictions and a reduction in calibration error, providing more reliable uncertainty estimates. The Expected Calibration Error (ECE) is reduced from $0.0095$ to $0.0026$ ($\approx73\%$) for IsoMaxPlus and $0.0033$ ($\approx65\%$) when combined with MC Dropout, compared to the baseline. Misclassified or underconfident predictions exhibit higher predictive
entropy and lower minimum distance scores, providing an interpretable metric for identifying unreliable predictions. These methods are well-suited for current and upcoming large-scale surveys, where reliable automated morphological classification and awareness of uncertainty are essential for identifying rare or previously unseen
galaxy morphologies.
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Materials Science
A nuclear-quantum-corrected machine-learning potential reveals quantum-enhanced hydrogen segregation at general grain boundaries in alpha-iron
Kazuma Ito
Atomistic descriptions of hydrogen
diffusion and trapping at defects are essential for understanding hydrogen embrittlement. As the lightest solute in metals, hydrogen exhibits
nuclear quantum effects that alter these processes even at room temperature. Explicit treatment of such effects is computationally demanding, limiting large-scale simulations of complex environments. Here, we use an Fe-H machine-learning interatomic potential (MLIP) based on the performant implementation of the atomic cluster expansion (PACE), covering diverse Fe-H environments, and relabel the training configurations underpinning its transferability with
quantum mean forces from centroid-constrained path-integral molecular dynamics at 300 K. This yields a
nuclear-
quantum-corrected PACE (NQC-PACE) without additional density functional theory calculations. At parent PACE, NQC-PACE describes
nuclear quantum effects on hydrogen trapping at vacancies, dislocations, surfaces and general grain boundaries, H-H interactions, and
diffusion in alpha-Fe. Grand-canonical Monte Carlo/molecular dynamics simulations show
nuclear quantum effects markedly enhance hydrogen segregation at general grain boundaries and trapping behaviour in closer agreement with experimental trends. This enhancement arises from selective
quantum stabilisation of open, anisotropically soft local environments. Our framework uses finite-temperature
quantum mean forces to relabel the configurational space covered by an MLIP, enabling large-scale analysis of complex materials where light-element
quantum effects matter.
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High Energy Astrophysical Phenomena
Broadband Properties of the Harmonic of Type-C Quasi-periodic Oscillation in MAXI J1348-630
Xin-Lei Wang, Zhen Yan, Jun-Feng Wang et al. (+3 more)
Harmonics are common features of quasi-periodic oscillations (QPOs) in black hole X-ray binaries; however, their physical origins remain poorly understood. Using broadband Insight-HXMT data, we investigated the Type-C QPO harmonic in MAXI J1348-630. The harmonic is significantly detected exclusively during the hard intermediate state and displays prominent energy-dependent properties: while it is strong in the soft X-ray band (< 10 keV) with its fractional rms amplitude even exceeding that of the fundamental QPO, it is much weaker in the hard X-ray band (> 10 keV), where its rms amplitude is generally several times lower than that of the fundamental. Furthermore, the harmonic shows no significant phase coupling with the fundamental in the soft X-ray band, whereas strong coupling is present in the hard X-ray band. These features point to a complex, energy-dependent origin for the harmonic. We propose that the hard X-ray harmonic may arise from nonlinear distortion of the fundamental waveform within the corona, while the soft X-ray harmonic is likely produced via a distinct physical process, such as the reflection emission from the inner disk.
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All authors Xin-Lei Wang, Zhen Yan, Jun-Feng Wang, Fu-Guo Xie, Zhan-Yi Liu, Ren-Yi Ma
Materials Science
Data-driven discovery and rapid, direct synthesis of MXenes
Ali Saffar Shamshirgar, Guilherme Ribeiro Portugal, Soheil Ershadrad et al. (+9 more)
MXenes, two-dimensional transition-metal carbides and nitrides, are typically obtained from MAX phases, yet historical reports suggest a broader, largely unexplored chemical space. Here we combine machine-learning-assisted database mining with experiments to uncover overlooked multilayer (ml) MXenes. Screening of repositories reveals a "Treasure Chest" of 38 previously synthesized but unrecognized ml-MXene candidates. Guided by these findings, we rediscover five MXenes using a rapid, scalable self-propagating high-temperature synthesis that requires no sustained external heating and completes within minutes. Inspired by the identified chemistries, we further realize 11 previously unexplored rare-earth-based M2CT2 MXenes (M= Pr, Nd, Sm, Gd, Tb, Ho, and Tm). Experiments and theory reveal semiconducting behavior and diverse
magnetic states across this family. Together, these results expand the MXene family and demonstrate a data-driven strategy for accelerating materials discovery through sustainable methods.
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All authors Ali Saffar Shamshirgar, Guilherme Ribeiro Portugal, Soheil Ershadrad, Roman Ivanov, Martin Dahlqvist, Florian Chabanais, Sanjay Chakraborty, Rainer Traksmaa, Irina Hussainova, Fredrik Heintz, Per O.Å. Persson, Johanna Rosen
Mathematical Physics · Cross-listed from math.RT
Nilpotent representations over equioriented cyclic quivers
Cornell Holmes and Mee Seong Im
We give a
geometric description of nilpotent representations of equioriented cyclic quivers over a field via an explicit bijection. Over a finite field, this yields formulas for the number of nilpotent representations and for the probability that a representation is nilpotent. We also give a refinement by rank. Over the Boolean semiring, we identify nilpotent semirepresentations with directed acyclic graphs, derive a recursive formula for their number, and determine the asymptotic decay rate of the probability of nilpotence.
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Quantum Physics
Quench Spectroscopy for Two-Dimensional Spin Models with Power-Law Interactions
Katharina Brechtelsbauer and Hans Peter Büchler
In this paper, we analytically compute the quench dynamics of simple product states that evolve under a
spin-1/2 XY-model with power-law interactions in a staggered
magnetic field. We use linear
spin-wave theory as well as a low-energy theory that accounts for strong phase fluctuations. This allows us to provide an analytic expression for the dynamics of phase-type correlations with short-range interactions, where the linear
spin-wave theory is known to fail. For density-type correlations the low-energy theory and the linear
spin-wave theory give the same result. Our analysis is valid for arbitrary
magnetic field strength and in particular provides an analytical understanding of the quench dynamics near criticality. Our results can thus provide useful tools for the experimental observation of excitation gaps and critical behavior.
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Materials Science
Strain control of mid-IR spectroscopic nonlinear photocurrents in PtSe$_2$
M. Gerlei, G. J. de Coster, J. Papp et al. (+4 more)
Semi-metallic noble-metal dichalcogenides are promising materials for infrared optoelectronics, yet the origin and tunability of their nonlinear optical responses remain poorly understood. Here, we demonstrate in-situ mechanical control of
photon-drag photocurrents in polycrystalline PtSe$_2$ thin films grown on flexible polyimide substrates. Using polarization-resolved mid-infrared photocurrent spectroscopy under uniaxial tensile strain, we observe pronounced strain-dependent changes in resistivity, photoconductivity, and helicity-dependent nonlinear photocurrents. The spectral response is consistent with optical excitations across the
spin-orbit-coupling-induced (SOC) band gap near the K point. We develop a theoretical framework attributing the photocurrent primarily to
photon-drag induced by
photon-momentum
symmetry breaking. Strain modifies its magnitude and polarization dependence through deformation potentials that tune the SOC-induced band gap. These results establish mechanical strain as a route toward reconfigurable infrared polarization detection.
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All authors M. Gerlei, G. J. de Coster, J. Papp, S. Heiserer, S. Schlosser, G. S. Duesberg, P. Seifert
Plasma Physics
New Formalism for Modelling Flowing Plasmas in a Magnetic Field
Subhasish Bag, Ashish Ganguli, Vikrant Saxena et al. (+2 more)
A new formalism for modelling a flowing
plasma in a
magnetic field, having potential for application in
plasma thrusters, materials processing, space
plasmas, etc., is developed. In this framework, the
plasma expands downstream from the source region into an expansion chamber along an axisymmetric
magnetic field. For
plasma flowing along a
magnetic field, the ion velocity parallel to the
magnetic field lines is much greater than the perpendicular velocity. This characteristic permits a unique ordering of the relevant flow variables when the flow equations are transformed into a
magnetic coordinate system (MCS), in which the coordinate axes are parallel and perpendicular to the field lines. The ordering of the flow variables in the MCS further simplifies the flow equations by allowing them to be split into sets of reduced equations. As a specific implementation, the proposed formalism was validated by using data (for boundary conditions) from a small volume
plasma system experiment (Ganguli et al 2016
Plasma Sources Sci. Technol. 25 025026). The model shows favourable agreement with the experiments and is used to predict various physical quantities relevant for applications. The corresponding physical implications are discussed in detail.
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All authors Subhasish Bag, Ashish Ganguli, Vikrant Saxena, Ramesh Narayanan, Debaprasad Sahu
Quantum Physics
Carnot Meets Quantum Information: A Thermal Machine Driven by Non-orthogonal State Discrimination
Tan-Ji Zhou, Yun-Qian Lin, Yu-Han Ma et al. (+1 more)
While the impossibility of perfectly identifying non-orthogonal states is a cornerstone of
quantum information science, they can nevertheless be distinguished with a finite error probability. Here, we propose a two-reservoir
quantum machine driven by such non-orthogonal-state discrimination to map its functional boundaries across the parameter space of the state overlap $\mu$ and the Carnot efficiency $\eta_C$. Within this $\eta_C$-$\mu$ plane, the machine exhibits phase-transition-like functional switching among a pure heat-engine phase, a mixed phase, and a dissipative phase. We identify critical thresholds governing these transitions: strong thermal driving ($\eta_C>0.5$) unconditionally guarantees positive work extraction, whereas weak driving ($\eta_C \lesssim 0.13$) induces an anomalous reentrant transition, where increasing $\mu$ unexpectedly restores engine functionality after a purely dissipative regime. Our results explicitly demonstrate how
quantum mechanics and thermodynamics jointly constrain information-to-energy conversion.
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All authors Tan-Ji Zhou, Yun-Qian Lin, Yu-Han Ma, C. P. Sun